Bump rexml from 3.2.8 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.8 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.8...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -58,16 +58,14 @@ GEM
     open4 (1.3.4)
     public_suffix (5.0.3)
     rchardet (1.8.0)
-    rexml (3.2.8)
-      strscan (>= 3.0.9)
+    rexml (3.3.9)
     ruby-ll (2.1.3)
       ansi
       ast
     ruby2_keywords (0.0.5)
     sawyer (0.9.2)
       addressable (>= 2.3.5)
       faraday (>= 0.17.3, < 3)
-    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     unicode-display_width (2.4.2)